Accurate Image On Paper (IOP) registration is generally desirable to users and consumers in the printing and/or image reproduction industry. Single-side (also referred to as “simplex”) IOP registration focuses on the location of image marks with respect to the edges of the paper. Also, double-sided (also referred to as duplex) or side 1 to side 2 IOP registration focuses on the location of image marks on side 2 with respect to corresponding image marks on side 1. The primary sources of simplex IOP registration error include the sheet registration module, the Raster Output Scanner (ROS) module, and the photoreceptor module. The precision and accuracy of these modules directly impact the simplex IOP registration. For duplex registration, in addition to the simplex sources, xerographic printers suffer from the shrinkage of paper during fusing. Basically, the paper is smaller when the duplex image is transferred than it was for the simplex image, effectively making the side 1 image smaller with respect to that of side 2. Also, there is significant variation in paper shrinkage within (sheet-to-sheet) and between different types of substrate media.
Contemporary setup procedures for IOP registration require calibration of image-on-paper (IOP) registration systems is often time consuming and cumbersome. Such procedures employ a separate image scanning device and a test pattern that includes a 2D grid of dots (a pattern of marks) on a central portion of a test sheet. For duplex registration the grid of dots is included on each side of the test sheet. The test pattern is scanned and the resulting image is processed to find the macroscopic location of the entire image with respect to two edges (a single corner) of the paper as well as the linear and non-linear magnification errors within the image. Such methods require the scanning device to be very precise and consistent (repeatable). Also those methods requires a calibration reference pattern to remove accuracy errors in the scan area. Accordingly, such contemporary methods do not lend themselves to an inline sheet fed image scanning device. Instead, the motion quality and controlled environment of an offline flatbed image scanning device is required to meet the required measurement precision and accuracy.
Measurements of an absolute IOP registration across a print, especially a large print, are prone to errors caused by the image scanning device measuring across long distances of the prints. Using a flatbed document scanner, a test pattern is measured with respect to a reference frame established at a single corner of the test paper and aligned with one of the edges of the print. Measurements are made across the large span of the print with the farthest being near the opposite corner of the print, relative to the reference corner. Often, this can be a very long distance considering some printers print onto 14.33″×22.5″ sheets. Positional errors in the scanned image (the test pattern) accumulate over long distances such that the errors in positional or location measurements using the scanned image are as significant as the errors in the test prints. Thus, in order to measure absolute locations over long spans such systems require a precision scanning device, such as a very repeatable flatbed scanner, and some calibration reference target that works to compensate or calibrate out the positional measurement errors across the two dimensional scan area.
Accordingly, it would be desirable to provide a system and/or method which can adjust the registration of an image transferred to sheets in an image transfer assembly, which overcomes the shortcoming of the prior art. In particular, a system and/or method that can adjust an image size, image shear, image target position and/or image target orientation of a transfer image based on an accurate scan of a preliminary image on a sheet.